1. Field of the Invention
The present invention is related to an electronic apparatus, and more particularly to an electronic apparatus comprising a printed circuit board (PCB) with variable quantities of memories therein.
2. Description of the Related Art
As printed circuit board (PCB) technology advances so that electronic apparatuses made therefrom may operate faster and be designed more densely, electromagnetic interference (EMI) problems for electronic apparatuses have increased. For example, in an electronic apparatus, a memory with high data rate may induce reflection effects at signal paths between the memory and a controller thereof when the memory is accessed by the controller. Therefore, I/O pins of a memory with on-die termination (ODT) or damping resistors disposed on the signal paths between the controller and the I/O pins of the memory without ODT are generally used to decrease the reflection effects.
Nowadays, more than one memory is implemented in an electronic apparatus, so as to provide larger data storage areas for complex applications. In order to simplify PCB design and reduce product complexity, a manufacturer may use a common PCB for various electronic apparatuses such as a low-end product with only one memory for providing basic functions or a high-end product with a plurality of memories for providing complex and advanced functions. However, not all of the I/O pins within a memory have ODT design for reducing reflection effects. Thus, parallel or series terminations are used on the signal paths of the I/O pins without ODT on the common PCB. Parallel termination means that a termination device and the signal path of one of the I/O pins without ODT are coupled in parallel on the common PCB. Series termination means that a termination device and the signal path of the one I/O pin without ODT are coupled in series on the common PCB. In general, series termination is the most popular design used due to low cost. However, if only one memory is required in an electronic apparatus with a common PCB that is designed for implementing a plurality of memories, the floating traces on the common PCB that are designed to couple the other memories may cause reflections due to antenna effect.
Therefore, a PCB that is designed to reduce reflections for implementing variable quantities of memories therein is desirable.